In a protection circuit on the primary side of a transformer used with a power unit, a fuse (primary fuse), generally a tubular fuse installed in a fuse holder, is used. To cope with the demand of the market for downsizing and weight-saving of a power unit, however, fuses have come to be directly surface-mounted on a wiring board. For this purpose, rather than a tubular fuse having a cylindrical glass casing, a rectangular chip fuse is often used, in which a linear or strip-shaped fuse element is mounted between the electrodes in a box-shaped ceramic casing. An example of prior art of such a box-shaped casing is disclosed in JP-2012-174443-A, known from which is a chip fuse composed of a fuse wire support made of ceramics and having a through hole along its center, a fuse wire mounted linearly across the through hole between the two opposed ends of the fuse wire support, a cylindrical ceramic casing in which the fuse wire support with the fuse wire as a fuse assembly is inserted, and metal caps located at both ends of the cylindrical body of the casing in electrical conduction with the fuse wire projecting from both ends of the fuse wire support.
Patent Publication 1: JP-2012-174443-A